The present invention relates generally to a means for regulating the high pressure component of a transcritical vapor compression system.
Chlorine containing refrigerants have been phased out in most of the world due to their ozone destroying potential. Hydrofluoro carbons (HFCs) have been used as replacement refrigerants, but these refrigerants still have high global warming potential. xe2x80x9cNaturalxe2x80x9d refrigerants, such as carbon dioxide and propane, have been proposed as replacement fluids. Unfortunately, there are problems with the use of many of these fluids as well. Carbon dioxide has a low critical point, which causes most air conditioning systems utilizing carbon dioxide to run transcritical under most conditions.
When a vapor compression system is run transcritical, it is advantageous to regulate the high pressure component of the system. By regulating the high pressure of the system, the capacity and/or efficiency of the system can be controlled and optimized. Increasing the high pressure of the system (gas cooler pressure) lowers the specific enthalpy at the inlet of the evaporator and increases capacity. However, more energy is expended because the compressor must work harder. It is advantageous to find the optimal high pressure of the system, which changes as operating conditions change. By regulating the high pressure component of the system, the optimal high pressure can be selected.
Hence, there is a need in the art for a means for regulating the high pressure component of a transcritical vapor compression system.
The present invention relates to a means for regulating the high pressure component of a transcritical vapor compression system.
A vapor compression system consists of a compressor, a heat rejection heat exchanger, an expansion device, and a heat absorbing heat exchanger. A suction line heat exchanger (SLXH) is employed to increase the efficiency and/or capacity of the system and prevent ingestion of liquid refrigerant into the compressor. In this preferred embodiment of the invention, carbon dioxide is used as the refrigerant. This invention uses this type heat of exchanger to regulate the high pressure component.
This invention regulates the high pressure component of the vapor compression (pressure in the gas cooler) by removing or delivering charge to/from the system and storing it in a storage tank of the suction line heat exchanger. A suction line heat exchanger exchanges heat internally between the high pressure hot fluid refrigerant discharged from the gas cooler (heat rejection heat exchanger) and the low pressure cool vapor refrigerant discharged from the evaporator (heat absorbing heat exchanger). There is a volume in these heat exchangers which is used by this invention to store refrigerant.
The high pressure in the gas cooler is regulated by adjusting valves in the suction line heat exchanger. A first valve allows excess charge from the gas cooler to flow into the storage tank if the gas cooler pressure is too high. If the gas cooler pressure is too low, a second valve is opened to release charge from the storage tank back into the system. By controlling the actuation of the valves, the high pressure component of the system can be regulated to achieve optimal efficiency and/or capacity.
Accordingly, the present invention provides a method and system for regulating the high pressure component of a transcritical vapor compression system.